This invention relates to a holographic recording method for obtaining a regenerated image having a high intensity of illumination.
Optimum exposure conditions for maximizing the intensity of the illumination of the regenerated image (such as the ratio of the amount of object light of the iluminated object and reference light, the amount of exposure and the like) are generally well known in the holographic recording art.
FIG. 1 gives the relationship between the size of an illuminated object and the regenerated image, which relationship is employed in accordance with the present invention, as will be explained in detail hereinafter. This relationship as shown in FIG. 1 was obtained by illuminating objects of different size with the same source of output light to form different holograms under the aforementioned optimum exposure conditions. A regenerated image was then obtained from each hologram by the same source of output light, after which the intensity of illumination thereof was measured. As can be seen in FIG. 1, when the size of illuminated object is decreased, for example, one half, the intensity of illumination of the regenerated image is increased more than three times. Thus, in accordance with the prior art, if the illuminated object and the holographic sensitive member for recording the object are each divided into two portions, respectively, respective half portions of the divided illuminated object may be recorded on respective half portions of the holographic sensitive member to form a hologram, as will be explained in more detail hereinafter with respect to FIGS. 2(a)-2(e). The hologram thus obtained, may be subjected to coherent regenerating light thereby regenerating the illuminated object. In this manner, the intensity of illumination of the regenerated image increases by more than 1.5 times when compared with the case where the illuminated object is recorded on the holographic sensitive member without dividing the illuminated object and hologram, as will now be explained in further detail.
In FIGS. 2(a)-2(e) for the sake of simplicity, the illuminated object and the holographic sensitive member are each segmented into two portions. As shown in FIG. 2(a), a first one half portion 1.sub.1 of an illuminated object 1 to be recorded as a hologram is recorded on a first one half portion 2.sub.1 of a holographic sensitive member 2 under the aforementioned optimum exposure conditions.
More specifically, portion 1.sub.1 is illuminated by an interferential beam 3 such as a laser beam, which is interfered with as object light 4 by reference light (not shown) on the holographic sensitive member 2. The portion 1.sub.1 is thus recorded as a hologram image. Thereafter, as shown in FIG. 2(b), the other half portion 1.sub.2 of the illuminated object 1 is illuminated by interferential beam 3 and recorded on the other half portion 2.sub.2 of the same holographic sensitive member 2 shown in FIG. 2(b).
Referring to FIG. 2(c), an image may be obtained from a split hologram 5, which corresponds to that obtained from member 2 of FIGS. 2(a) and 2(b). The intensity of illumination of the regenerated image is 1.5 times greater than that obtained when the illuminated object 1 is recorded on the holographic sensitive member 2 without dividing the illuminated object. This results from the fact that since the illumination intensity of the regenerated image of only one-half of object 1 would be three times greater than that of the entire object without dividing it in halves, the above illumination intensity must be divided by two in order to obtain the illumination intensity of the entire object when it is divided in halves.
When the whole illuminated object is to be regenerated, the hologram 5 may be wholly illuminated by regenerating light 6 as shown in FIG. 2(c) to obtain a regenerated image 7 having a boundary indicated at 8 and a lower portion 9. When the illuminated object is to be partially regenerated, a hologram portion 5.sub.1 (corresponding to portion 2.sub.1 of FIG. 2(a)) on which the desired information is recorded may be illuminated by regenerating light 6 whereby a regenerated image portion 7.sub.1 may be obtained, as shown in FIG. 2(d). In this manner, unnecessary portions need not be regenerated, and hence, this method is particularly effective for information retrieval. However, there is a shortcoming in this method in that, when regenerating light 6 is directed onto hologram portion 5, with the intention of obtaining a regenerated image of the object portion 1.sub.1, the regenerating light decreases in quantity if the light is slightly displaced with respect to hologram portion 5.sub.1, as shown in FIG. 2(e). Thus, the image portion corresponding to portion 7, is substantially darkened with respect to that of FIG. 2(d) due to the partial presence of image portion 7.sub.2. Further, whenever hologram 5 is progressively scanned by a regenerating light beam to obtain regenerated image 7, the intensity of illumination of image portion 7.sub.1 will fluctuate.